1. Field of the Invention
The present invention relates to a variable capacity swash plate type compressor for compressing refrigerant gas, adapted for being accommodated in a climate control system of vehicles.
2. The Description of the Related Art
Japanese Unexamined Patent Application No. 63-186973 discloses a typical variable capacity swash plate type compressor in which a housing assembly includes a cylinder block, and front and rear housings. The housing assembly defines therein a crank chamber, a suction chamber, a discharge chamber, and a plurality of cylinder bores fluidly communicated with the crank, suction, and discharge chambers. Each of the cylinder bores receives a reciprocatory piston. The housing assembly mounts therein a drive shaft so as to be rotatably supported via axially spaced a pair of anti-friction bearings. On the drive shaft a rotor or a drive plate is mounted to be rotated together with the drive shaft within the crank chamber. The rotor is provided with a guide means for smoothly guiding the pivoting motion of a swash plate, and therefore, the guide means is connected to a guided means of the swash plate at a position thereof which can be referred to as the top dead center of the swash plate. Thus, the swash plate can be rotated synchronously with the rotor about the axis of rotation of the drive shaft. The drive shaft is fitted with a sleeve element on which the swash plate is pivotally held. Namely, the swash plate is pivoted about a given axis which is perpendicular to a plane defined by the axis of rotation of the drive shaft and the top dead center of the swash plate, so as to change an angle of inclination thereof with respect to a plane perpendicular to the axis of rotation of the drive shaft. The swash plate supports thereon a wobble plate via a thrust bearing so that the wobble plate is prevented by a rotation-preventing means from being rotated with the swash plate. The wobble plate is engaged with one end of each of a plurality of piston rods having the other ends thereof connected to the reciprocatory pistons. The wobble plate and respective piston rods acts as a mechanism for converting the rotating motion of the swash plate to the reciprocating motion of the respective pistons in the cylinder bores.
The housing assembly is also provided with a capacity control valve housed in a portion thereof, which can detect the suction pressure of a refrigerant gas and can introduce the compressed refrigerant gas at a discharge pressure into the crank chamber.
When the drive shaft is rotated by a drive force transmitted from e.g., a vehicle engine via a solenoid clutch device, the swash plate at a given angle of inclination is rotated together with the drive shaft. Thus, the rotation of the swash plate is converted by the wobble plate and the piston rods into the reciprocation of the pistons in the respective cylinder bores. Therefore, the refrigerant gas is sucked from the suction chamber into the cylinder bores where the refrigerant gas is compressed. When the refrigerant gas is compressed in the respective cylinder bores, it is discharged toward the discharge chamber.
During the compressing operation of the compressor, when the suction pressure of the refrigerant gas decreases, the capacity control valve detects a reduction in the suction pressure, and permits the compressed refrigerant gas to flow from the discharge chamber into the crank chamber thereby causing an increase in the pressure level within the crank chamber. An increase in the pressure level in the crank chamber causes an increase in a back pressure acting on the respective pistons so as to decrease the reciprocating stroke of the respective pistons. Thus, the angle of inclination of the swash plate is reduced, and the discharge capacity of the compressor reduces.
On the contrary, when the suction pressure of the refrigerant gas increases, the capacity control valve stops passing the compressed refrigerant gas at a discharge pressure from the discharge chamber into the crank chamber, and accordingly, the pressure level in the crank chamber is reduced so as to reduce the back pressure applied to the respective pistons. Thus, the reciprocating stroke of respective pistons increases causing an increase in the angle of inclination of the swash plate. Therefore, the discharge capacity of the compressor increases.
When the angle of inclination of the swash plate of the above-described compressor increases and the swash plate comes into abutment against the rotor, the angle of inclination of the swash plate stops increasing.
On the contrary, when the angle of inclination of the swash plate decreases and the swash plate comes into abutment against a circlip element or a washer element fixedly mounted on the drive shaft, the washer element stops the angle of inclination of the swash plate decreasing. The smallest angle of inclination of the swash plate is generally set at angle larger than 0 degree, i.e., at several degrees so that the smallest capacity of the compressor may be approximately 10%.
Nevertheless, when the above-described refrigerant compressor is supplied with a drive force by the vehicle engine via the solenoid clutch so as to rotate the drive shaft, the compressor compresses the refrigerant to exhibit at least a small discharge capacity even when the thermal load applied to the compressor, and the suction pressure of the refrigerant gas, are very small. Therefore, the capacity control valve constantly detects the suction pressure and acts to introduce the compressed refrigerant gas, at a given discharge pressure, into the crank case. Thus, when the rotational speed of the drive shaft of the compressor is high, the pressure level in the crank chamber instantly increases, resulting in an adverse affect on the sealing performance of a shaft sealing device mounted on the drive shaft.
Taking into account this adverse affect, if the compressor is assembled so as to have a swash plate thereof set in such a manner that the smallest angle of inclination of the swash plate is 0.degree. without any consideration of the shape and the center of gravity of the swash plate, the compressor can neither exhibit compression performance under a particular condition such that pressure in the crank chamber is balanced with the suction pressure, nor return to a high capacity operation from the smallest discharge capacity operation (i.e., capacity at 0%) under the conditions of a low thermal load and a high rotating speed of the drive shaft.
Further, when the solenoid clutch is disengaged so as to stop transmission of the drive force from the vehicle engine to the drive shaft of the compressor, a driver of the vehicle must often have an uncomfortable feeling when the solenoid clutch is engaged. In addition, mounting of the solenoid clutch on the vehicle to control the transmission of the drive force from the vehicle engine to the refrigerant compressor contributes to an increase in the weight of vehicle per se, an increase in an electric power consumption, and a deterioration of fuel consumption of the vehicle.